1. Field of the Invention
The present invention is directed to a method and apparatus (e.g., power supply) for powering a device (e.g., lamps producing ultraviolet light such as electrodeless lamps) at substantially higher power levels than have previously been possible, and/or powering such device (e.g., lamp) at normal power levels but with reduced cooling requirements, or with combinations of power levels higher than conventional power levels with cooling air pressure and flow requirements lower than that conventionally used. The present invention is also directed to a method and apparatus for powering a magnetron at substantially higher power levels and/or reduced cooling requirements. In particular, the present invention is directed to a method and apparatus (e.g., power supply) wherein ultrahigh power levels may be achieved for faster ultraviolet light curing, and/or reduced cooling costs may be achieved.
2. Discussion of Related Art
While it has been desired to utilize higher power levels for increasing speed and productivity in many ultraviolet light curing applications (e.g., for curing polymer material with ultraviolet light), various practical constraints may restrict the ability to go to higher power levels of a power supply, to power the ultraviolet light lamp system, than those conventionally used.
For example, ferro-resonant 50 or 60 hertz power supplies may produce high ripple magnetron current waveforms with peak currents that are much higher than the average current. Rectified alternating current power supplies may produce a magnetron current waveform also with high ripple at 100 or 120 hertz. The upper power level may be limited by the peak component in this waveform. Thus, when powering a magnetron at substantially higher power levels and/or reduced cooling requirements, and the peak current component approaches the upper power limit of the magnetron, disadvantageous magnetron moding may occur.
Another practical constraint is the magnetron cost. Magnetrons operating at 2450 MHz are widely used in the heating or xe2x80x9ccooker industryxe2x80x9d with power levels up to about 3000 watts. Because of the widespread use, they may be produced in large quantities, and have a relatively low price. However, there are no magnetrons in this price range that are designed to operate over 3000 watts. The cost of magnetrons currently on the market in the over-3000 watt range may be many times more expensive, and are mainly used in radar-type applications.
Another constraint on increasing the power level is magnetron size. Magnetrons currently available to operate at more than 3000 watts are generally water-cooled, which may add a utility requirement that increases complexity and operating cost. Higher power magnetrons are generally much larger in physical size, and may require extensive lamp redesign and larger and less desirable lamp dimensions.
Another constraint on increasing power level is magnetron overheating. The air cooling requirements to maintain reliable operation of present-day magnetrons in use are already aggressive at power levels below 3000 watts of microwave energy. As the power level is increased, the cooling air pressure and flow requirements may increase at a much faster rate than power. FIG. 1 is a graph showing magnetron cooling requirements at a steady state operation. The dotted line represents the cooling for high ripple supply current. Even small increases in steady-state power may require large increases in magnetron cooling.
A still further constraint on power level is bulb overheating. The quartz envelope of microwave-driven electrodeless lamps may require aggressive cooling to operate at high power levels. As the power level is increased, the cooling air pressure and flow requirements increase at a much faster rate than power. FIG. 2 is a graph showing bulb cooling requirements at a steady state operation. The dotted line represents the bulb cooling for a high ripple magnetion current. The cooling power requirements for current state-of-the-art equipment is already large and noisy, and even small increases in power may require large increases in bulb cooling. In many applications, large increases in air cooling are not acceptable.
It was previously known to those skilled in the art that pulsing or flashing a lamp on can allow operation at much higher power levels during the high power cycle phase. This is in essence a pulsed, or flash, technique. There are many references in the literature, and in the market, of examples, such as pulsed Xenon ultraviolet lamps, using variations of this technique. In this technique of pulsing or flashing a lamp on, however, the duration of the xe2x80x9conxe2x80x9d pulse, or high-power cycle in Xenon flash lamps, is very short (in the range of 1 ms), with much longer xe2x80x9coffxe2x80x9d times between the high-power flashes. The rates of each xe2x80x9con-and-offxe2x80x9d period must be relatively very fast in order to prevent plasma extinction that will occur in a fraction of a second, or the apparatus must have special ignition schemes to re-ignite the bulb for each flash. Microwave-powered, medium-pressure electrodeless lamps, and linear medium-pressure arc lamps, used for ultraviolet curing, may require extended delays before the lamp can be restarted if the plasma in the hot bulb is allowed to extinguish. Restarting the bulb plasma may then become extremely difficult and time consuming, requiring a significant waiting period to allow for the bulb to cool down, and the fill within the bulb to condense.
U.S. Pat. No. 5,838,114 to Penzenstadler et al., the subject matter of which is incorporated herein by reference, addresses the problem of quickly restarting an electrodeless lamp. A low power level or simmer mode may be employed. This allows the lamp to be momentarily switched to a much lower power level, with less than 10% of full power operation, and allows the lamp to be switched back to full power operation at any time. The patent teaches switching from a relatively high power to a relatively low power to obtain the quick restart feature. The patent also discloses a power supply that achieves this switching from the relatively high power, supplied to the magnetron in a full power mode, to the relatively lower power, where the lower power is of a magnitude to generate sufficient microwave radiation to maintain the lamp in an ignited condition. The patent further discloses the xe2x80x9crelatively high powerxe2x80x9d as a normal power level as conventionally used in the art.
U.S. Pat. No. 5,838,114 provides no disclosure as to modification of bulb cooling requirements in the cycling mode.
U.S. Pat. No. 5,838,114 discloses cycling wherein the relatively high power mode is the power level that is conventionally used. The highest power electrodeless lamp systems currently available for commercial use are 6-inch and 10-inch linear lamp systems that use magnetrons desired to operate at about 2800 watts. With a typical highly coupled linear lamp system, this yields about 450 average watts/inch on the 6-inch long lamp system, and 560 average watts/inch using two of the same magnetrons each operating at 2800 watts on 10-inch systems.
FIG. 3 is a chart showing the relative UV light output for several systems where systems A and B represent currently available lamp systems for commercial use. FIG. 3 shows power levels of 1800 W rf and 2800 W rf, respectively, for Systems A and B, which are power levels of the magnetron output. As the magnetrons are about 70% efficient, the power levels of the magnetron are about 70% of the power levels of the power supplied to the magnetron from the power supply. Throughout this disclosure, the reported quantitative power levels are power levels of the magnetron output, discussed as power output, which is about 70% of the actual output of the power supply. That is, the power level from the power supply itself is 30% higher.
Embodiments of the present invention may provide a power supply for a lamp system. The power supply may include structure to switch from a high power level to a low power level. The high power level and the low power level together are a cycle that is repeated. The high power level is higher than the conventional steady-state power level used for the same lamp system. The power supply may provide low ripple power.
The lamp system may be an electrodeless ultraviolet lamp system with an electrodeless bulb. The lamp system may also be an arc lamp system for powering an arc lamp outputting ultraviolet light.
Embodiments of the present invention may also provide a power supply to provide reduced cooling requirements for the lamp system. The power supply may include structure to switch from a first power level to a second power level lower than the first power level. The first and second power levels together form a cycle that is repeated. The power supply may also include structure to cool the lamp system where the level of cooling of the lamp system is reduced as compared to cooling requirements of the same lamp system. The power supply may operate in a steady-state condition at the first power level.
Embodiments of the present invention may still further provide a method of operating a power supply for powering a lamp system. The method may include switching the power supplied by the power supply to the lamp system between a high power level and a low power level. The high power level and the low power level together form a cycle that is repeated. The high power level is larger than a conventional steady-state power level for powering the lamp system.
Other embodiments, advantages and salient features of the invention will become apparent from the following detailed description taken in conjunction with the annexed drawings, which disclose preferred embodiments of the invention.